Investigations are carried out to determine critical conditions for changes in biological systems produced by ultrasound. Experimental work is carried out on selected cellular, intracellular and macromolecular systems in collaboration between physically and biologically trained scientists. Much emphasis is placed on design of experiments according to available knowledge, and analysis of results to determine basic principles involved. Physical and biophysical theory are developed where required, and experiments on model systems carried out to test hypotheses. The broad aim is to develop methods for calculating parameters (frequency, amplitude-distribution or intensity-distribution, pulse regime, time of irradiation, etc.) of an ultrasonic field which lead to specified changes in given biological systems.